1. Field of the Invention
The present invention relates to a method for reinforcing structural supports and to reinforced structural supports. More particularly, the present invention relates to the use of high strength fabrics to reinforce beams and connections between beams and other structural members such as platforms, supports for decks, and supporting columns and structures.
2. Background of the Related Art
Construction methods in which elevated platforms are supported by beams which are in turn supported by vertical columns, are used extensively in multilevel parking garages, bridges, freeway overpasses, multilevel commercial and residential construction, and the like. The columns, beams, and platforms are often constructed of steel reinforced concrete.
During an earthquake or other event that produces atypical stresses, these concrete beams are particularly prone to fracture and spalling where they are connected to their supporting vertical columns and where they are connected to the elevated roadway platform. This is because structural members are often exposed to the greatest localized stresses at the point they connect to other structural members. Tests indicate that when these members fail, fractures typically propagate at a 45.degree. angle from perpendicular connections. Once a fracture has begun in a concrete member, it progresses rapidly. In an earthquake, continued shaking can quickly cause the fractured concrete member to spall and crumble, resulting in catastrophic failure. Even where the failure is not catastrophic, fractures in the structural members can compromise the structural integrity such that the entire structure must be demolished and rebuilt at great cost. Also, beams and columns may be weak due to corrosion of reinforcing steel, increased weights on structuresized design, the use of low-strength concrete in the original construction, and other problems.
Although the strength of structural members can be increased by increasing the size of those members, increasing the size of structural members used in elevated roadway construction is both extremely expensive and is inapplicable to retrofit work.
Recent events have demonstrated the vulnerability of many existing structures to earthquakes. In the last 20 or so years, the area around Los Angeles, Calif. has experienced an increase in both the frequency and magnitude of earthquakes. It is expected that this increased seismic activity will continue or even increase still further. Accordingly, critical efforts are underway to identify methods of retrofitting structures to improve their ductility and strength. Methods that do not change the stiffness characteristics of the structure are highly preferred.
The use of high strength fabrics to reinforce vertical columns is known. One method of reinforcing vertical concrete support columns is set forth in U.S. Pat. No. 5,043,033, issued to Fyfe. In this patent, the surface of a concrete column is wrapped with a composite material to form a hard annular shell surrounding the concrete column. The space between the outer composite shell and the concrete column is then pressurized by injecting a hardenable liquid.
Another approach to reinforcing the exterior of an existing concrete support column is set forth in U.S. Pat. No. 5,218,810, issued to Isley, Jr. In this patent, the exterior surface of a concrete column is wrapped with a composite material to form a hard annular shell or sleeve which is in direct contact with the column surface.
Wrapped steel sheets are also used to reinforce vertical columns. In this method a steel sheet is wrapped around the column, with the ends of the steel sheet being welded or otherwise joined to form a continuous steel band encircling the column. One disadvantage to this method is that these steel wraps must be maintained to prevent corrosion. Another disadvantage is that this method increases the stiffness of the member.
None of these methods address the problem of reinforcing horizontal beams where they connect with vertical support columns or roadway platforms. The topology of such connections makes reinforcing these connections and structural members difficult. A need exists therefore for a method to economically reinforce beam-to-column and beam-to-platform connections and increase the ductility of structural members at and around those connections, both in new construction as well as in retrofit applications.
Accordingly, it is an object of this invention to provide reinforced structural connections.
It is a further object of this invention to provide a method of retrofitting existing structures to provide additional strength at beam-to-column and beam-to-platform connections.
It is a further object of this invention to provide a structure with reinforced beam-to-column and beam-to-platform connections for new construction.
It is a further object of this invention to reinforce structural beams along an axis that is approximately 45.degree. from the angle of intersection with a supporting column.
It is a further object of this invention to provide a means by which damaged structures may be repaired, thereby strengthening them and obviating the need to demolish and reconstruct them.
These and other objects and features of the present invention will become better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings.